Expandable wellbore stabiliser

ABSTRACT

A stabiliser is disclosed for stabilising a radially expandable tubular element extending in a wellbore drilled into an earth formation. The stabiliser comprises a radially expandable tubular member selected from a section of the tubular element and a sleeve surrounding the tubular element, and at least one stabiliser arm connected to the tubular member, each arm being movable from a radially retracted position to a radially extended position by the action of a spring force. The stabiliser further comprises locking means arranged to lock each arm in the retracted position when the tubular element is in the unexpanded form and to unlock the arm upon radial expansion of the tubular member so as to allow the arm to move to the extended position thereof.

FIELD OF THE INVENTION

The present invention relates to a stabiliser for stabilising a tubularelement extending in a wellbore drilled into an earth formation. Thetubular element is, for example, a casing, which is to be cemented inthe wellbore. Generally it is desirable that the casing is positionedcentrally in the wellbore before and during cementing in order to ensurethat the annular cement layer between the casing and the wellbore wallprovides sufficient isolation both in radial and longitudinal direction.In the specification hereinafter the terms “stabiliser” and“centraliser” are used, both referring to the same meaning.

BACKGROUND OF THE INVENTION

Various types of centralisers have been applied to stabilise andcentralise a tubular element, such as a casing, in a wellbore. One suchcentraliser is a bow centraliser, which is provided with spring-typearms extending against the wellbore wall. However, such knowncentralisers are less applicable for tubulars which are to be radiallyexpanded in the wellbore.

SUMMARY OF THE INVENTION

In accordance with the invention there is provided a stabiliser for aradially expandable tubular element extending in a wellbore drilled intoan earth formation, the stabiliser comprising a radially expandabletubular member selected from a section of the tubular element and asleeve surrounding the tubular element, and at least one stabiliser armconnected to the tubular member, each arm being movable from a radiallyretracted position to a radially extended position by the action of aspring force, the stabiliser further comprising locking means arrangedto lock the arm in the retracted position when the tubular element is inthe unexpanded form and to unlock the arm upon radial expansion of thetubular member so as to allow the arm to move to the extended positionthereof.

It is thereby achieved that, upon radial expansion of the tubular memberin the wellbore, the tubular member stretches in circumferentialdirection so that the locking means becomes unlocked and each arm ismoved by the spring force to its radially extended position. The armsthereby become biased against the wellbore wall and stabilise/centralisethe tubular element in the wellbore.

Suitably each arm is integrally connected to the tubular member, and thespring force stems from elastic deformation of the arm relative to themember element when the arm is in its retracted position.

To enable easy installation of the tubular element in the wellbore, itis preferred that the arm, when in the retracted position thereof,extends in substantially circumferential direction of the tubularmember.

Preferably the stabiliser comprises a plurality of said arms includingat least two said arms located at substantially the same circumferentialposition and at selected mutual axial spacing.

To achieve adequate centralising of the tubular element in the wellbore,suitably the stabiliser comprises a plurality of said arms including atleast three arms at selected mutual circumferential spacing.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention will be described hereinafter in more detail and by way ofexample with reference to the accompanying drawings in which:

FIG. 1 schematically is a perspective view of an expandable tubularelement provided with an embodiment of a stabiliser according to theinvention;

FIG. 2 schematically shows cross-section 2—2 of FIG. 1;

FIG. 3 schematically shows the tubular element of FIG. 1 after radialexpansion thereof; and

FIG. 4 schematically shows view 4—4 of FIG. 3.

DETAILED DESCRIPTION OF THE INVENTION

Referring to FIGS. 1 and 2 there is shown a tubular element in the formof a casing 4, prior to radial expansion thereof, of a wellbore (notshown) formed in an earth formation. The casing 4 is provided with astabiliser 6 for stabilising and/or centralising the casing 4 in thewellbore. The stabiliser 6 includes a radially expandable tubular memberin the form of a sleeve 8 surrounding the casing 2. The sleeve 8 isprovided with longitudinal slots 10 (only some of the slots are shownfor ease of reference) which are overlapping in longitudinal directionso that only a low expansion force is required to radially expand thesleeve 8. Furthermore, the sleeve 8 is provided with three cut-outportions 12, 12′, 12″ regularly spaced along the circumference of thesleeve 8, whereby in FIG. 1 only one cut-portion 12 is shown for ease ofreference. The two other cut-out portions 12′, 12″ are similar in shapeand size to cut-out portion 12.

Cut-out portion 12 is formed of four rectangular cut-out sections 14,15, 16, 17 which are interconnected by a longitudinal cut 18. Thecut-out sections 14, 15, 16, 17 and longitudinal cut 18 define threerectangular arms 19, 20, 21 integrally connected to the remaining partof sleeve 8.

The longitudinal cut 18 extends inclined relative to the circumferentialdirection of the sleeve 8 thereby defining inclined circumferential endsurfaces 24, 26, 28 of the respective arms 19, 20, 21 and complementaryinclined circumferential end surface 30 of the remaining part of sleeve8.

As shown in FIG. 2, the inclined end surfaces 24, 26, 28 of the arms 19,20, 21 are locked behind the inclined end surface 30 of the remainingpart of the sleeve 8, thereby retaining the arms 19, 20, 21 in aradially retracted position. Each arm 19, 20, 21 has been plasticallydeformed in a manner that the arm assumes a radially extended position(as shown in FIG. 3) when no longer radially retracted, and that the armis subject to elastic deformation when radially retracted (as shown inFIG. 2).

Reference is further made to FIGS. 3 and 4 showing the casing 4 andstabiliser 6 after radial expansion of the casing 4 and sleeve 8. Theinclined end surfaces 24, 26, 28 of the arms 19, 20, 21 are no longerlocked behind the inclined end surface 30 of the remaining part of thesleeve 8, and as a result the arms 19, 20, 21 extend in their respectiveradially extended positions.

During normal operation the casing 4 is provided with the stabiliser 4whereby the sleeve 8 is arranged around the casing 4 and the arms 19,20, 21 are in their retracted positions. Subsequently the casing islowered into the wellbore and radially expanded by, for example, pullingor pushing an expander through the casing 4. Cement slurry is pumpedinto the annular space between the wellbore wall and the casing 4 beforeor after expansion of the casing 4.

As the casing 4 radially expands, the sleeve 8 is also radiallyexpanded. The slots 10 of the sleeve 8 thereby open up so that the forcerequired to expand the sleeve is relatively low. The sleeve 8 stretchesin circumferential direction as a result of its radial expansion, andthereby the inclined end surfaces 24, 26, 28 of the respective arms 19,20, 21 become unlocked from the inclined end surface 30 of the remainingpart of the casing 4. Each arm 19, 20, 21 springs radially outwardagainst the wellbore wall upon unlocking of its inclined end surface 24,26, 28 from end surface 30 due to release of the elastic deformationenergy contained in the arm when the arm is radially restrained. Theradial position of the arms 19, 20, 21 after unlocking is shown in FIG.3.

The arms 19, 20, 21 are dimensioned such that the tips of the arms,after unlocking of the arms, become biased against the wellbore wall andthereby centralise and stabilise the casing 4 in the wellbore.

Instead of the sleeve being provided with longitudinal slots, the sleevecan be provided with a configuration of holes.

Furthermore, instead of cementing the casing in the wellbore, one or anumber of alternative annular sealing means can be applied in theannular space between the casing and the wellbore wall.

While the illustrative embodiments of the invention have been describedwith particularity, it will be understood that various othermodifications will be readily apparent to, and can be easily made by oneskilled in the art without departing from the spirit of the invention.Accordingly, it is not intended that the scope of the following claimsbe limited to the examples and descriptions set forth herein but ratherthat the claims be construed as encompassing all features which would betreated as equivalents thereof by those skilled in the art to which thisinvention pertains.

1. A stabiliser for a radially expandable tubular element extending in awellbore drilled into an earth formation, the stabiliser comprising aradially expandable tubular member, and at least one stabiliser armconnected to the tubular member, each arm being movable from a radiallyretracted position to a radially extended position by the action of aspring force, the stabiliser further comprising locking means arrangedto lock the arm in the retracted position when the tubular element is inthe unexpanded form and to unlock the arm upon radial expansion of thetubular member so as to allow the arm to move to the extended positionthereof.
 2. The stabiliser of claim 1, wherein the arm is integrallyconnected to the tubular member and wherein the spring force stems fromelastic deformation of the arm relative to the member element when thearm is in the retracted position thereof.
 3. The stabiliser of claim 2,wherein the arm is defined by a cut-out portion of the tubular member.4. The stabiliser of claim 3, wherein the arm, when in the retractedposition thereof, extends in substantially circumferential direction ofthe tubular member.
 5. The stabiliser of claim 2, wherein the lockingmeans comprises a circumferential end surface of the arm, said endsurface extending inclined relative to the circumferential direction ofthe tubular member.
 6. The stabiliser of claim 5, wherein the lockingmeans further comprises a circumferential end surface of the tubularmember, which end surface is inclined relative to the circumferentialdirection of the tubular member, the respective end surfaces of the armand the tubular member having complementary inclinations.
 7. Thestabiliser of claim 1, comprising a plurality of said arms including atleast two said arms located at substantially the same circumferentialposition and at selected mutual axial spacing.
 8. The stabiliser ofclaim 1, comprising a plurality of said arms including at least threearms at selected mutual circumferential spacing.
 9. The stabiliser ofclaim 1, wherein the tubular element is a casing extending into thewellbore.
 10. The stabiliser of claim 1 wherein the radially expandabletubular member is selected from a section of the tubular element and asleeve surrounding the tubular element.
 11. The stabiliser of claim 10,wherein the sleeve is an expandable slotted tubular member.